Typical power generation systems, which are designed to generate DC power by means of a power generator such as a fuel cell and convert the DC power into AC power by means of an electric power convertor such as an inverter, are used being interconnected to a system power supply. In the power generation systems embodied in such a form, electric power generated by the power generator and electric power transmitted from the system power supply are supplied to an external electric power load (e.g., home electric power).
Power generators such as fuel cells for generating DC power are slow in the speed of changing the output rate in accordance with load variations in the external electric power load. Therefore, surplus electric power is generated, causing reverse power flow toward the system power supply, in cases where the total power consumption of all the appliances supplied with power from the power generation system is lower than the output power of the power generation system. There have been known power generation systems capable of preventing or mitigating the reverse power flow (see Patent Document 1 and Patent Document 2).
According to the power generation system disclosed in Patent Document 1, in a case where the output of the inverter is stopped when surplus electric power is generated, a system interconnection failure occurs, etc, the DC power generated in the power generator is supplied to a DC power load through a first DC/DC convertor arranged in parallel with the inverter to consume the surplus electric power. In this way, reverse power flow can be prevented in a case where the output of the inverter is stopped when surplus electric power is generated, a system interconnection failure occurs, etc.
In the fuel cell system disclosed in Patent Document 2, in the event of an occurrence of surplus electric power, the DC power generated in the fuel cell is supplied to a DC power load connected to an inverter to consume the surplus electric power. FIG. 4 is a block diagram that schematically shows a configuration of the power generation system of Patent Document 2 shown in FIG. 1.
As shown in FIG. 4, this fuel cell system has a fuel cell 101, a DC/DC convertor 102 for receiving and converting DC power from the fuel cell 101, and a DC/AC convertor (inverter) 103 for converting the output of the DC/DC convertor 102 into AC power. The output side of the DC/AC convertor 103 is connected to a system power supply 106 at an interconnection point 107 by a power supply wire 110. Connected to the interconnection point 107 is an external AC power load 109. Connected to the power supply wire 110 is an internal AC power load (heater) 104. That is, the AC power load 104 is connected to the output side from which the AC power derived from the fuel cell 101 of this fuel cell system is output. The electric wire for connecting the system power supply 106 and the interconnection point 107 is provided with a current detector 105 for detecting a current flowing between the system power supply 106 and the interconnection point 107. The current detected by the current detector105 is input to a controller 108. The controller 108 puts the internal AC power load 104 into operation if the direction of the current detected by the current detector 105 is from the interconnection point 107 to the system power supply 106. As a result, the surplus electric power, which has occurred in the fuel cell 101, is consumed in the form of AC power by the internal AC power load 104, whereby an occurrence of reverse power flow can be prevented.
Patent Document 1: JP-A-2006-67757 (see particularly FIG. 1)
Patent Document 2: JP-A-2006-12563 (see particularly FIG. 1)